I drive a 2004 Zen VXi. In the last 7 months, I have done about 10.8k kms. Just got the third service (Oil Filter + Oil Change) done at 10k kms. The scheduled service did wonders to the car and it was smoother than ever before. Even the FE in city driving conditions went up to 16 kms/ltr.

Lately, I have noticed that the car tends to heat up quickly. With just about ~3 kms of driving, the radiator fan comes on and the car feels rough. Even during idling with radiator fan off, slight vibrations are felt. This wasn't the case before. Idling was smooth and it was difficult to tell if the engine was ON. Overheating here doesn't indicate an increase in internal engine temperature. The temperature gauge remains at the normal range with any amount of driving. It's just that the car feels rougher and the engine feels warmer. Opening the engine bay feels like stepping into a furnace. I have checked the engine oil and coolant level and they seem perfect.

If I don't drive the car for 2 to 3 days at a stretch, this problem seems to disappear. The car feels smooth and idling is normal. It comes back after I have run the car for more than 150 kms at a stretch (my runs to Pune).

I know that ambient temperature plays a lot with the engine cooling system. But what can explain the rough idling and returning to normalcy with no driving for 3 days? Do you think there some latent heat build up inside the engine that takes time to cool? Or is it that the engine oil is taking time to cool? Also, does a hot engine feel rougher than an engine at optimum operating temperature? Have you guys faced anything like this with your cars?

Automotive Maruti says heating quickly is just normal in this weather. Iím not convinced. Your opinions are highly appreciated.

ur engine is perfectly okay,as long as your temperature gauge doesnt indicate it
when the car is in motion ,the air flow does help in cooling it.so when ur stationary,the fan comes on to do the cooling .

We have a 02 zen vxi, the heating is normal in the car as long as the temp gauge needle is in the safe zone and there's nothing to worry if the fan's comin on. The new zen does heat up a bit, in our car the front wheels also get quite hot, but the brake's not binding. As for rough idling do what sppedsatya has told you.

Thanks for your insights on the problem plaguing my car. Using the reasons you described as a checklist, I find that:

shortage of fuel in the tank -> Car is always tanked up. Least it goes is half-tank.
Clogged air filter -> Got the car serviced just 2 weeks back @ 10k kms. Can the air filter get clogged so soon?
leaky manifold,throttle body or cylinder head gasket -> Somewhere on the net, I read the same thing. A failing head gasket could cause the car to have rough idling and overheat. But is this possible @ just 10k kms, and that too with at least 8k kms of highway driving? Leaky manifold or leaky throttle body are unlikely since there is no carb. Fuel supply to the engine is mpfi.

defective spark plug -> Again, isn't 10k kms too early for spark plugs to conk off. Anyway, I will bear this in mind and get it checked.
leaky /disocnnected HT cord -> Didn't quiet get this. Forgive my ignorance, but what's the HT cord?
improper ignition timing -> Doesn't the 16-bit computer take care of this in MPFI cars?

clogged injectors -> Can the injectors get clogged in just 2 weeks?

Another factor, that I think, that might be causing the abovesaid problems could be bad fuel. Adulterated or lower quality fuel could cause the engine to heat up faster and cause rough idling. However, the car pickup seems just normal. But the chances are less since I fill up the same fuel (XtraPremium) from the same pump, everytime.
I drove the car today after giving it two-days of rest. Although the idling vibrations still exist, they have reduced and the car did not overheat today with even 30 kms of driving. It's funny how even a little depart from perfection in our cars (read loved babes) can get us worked up!

did you check with the fan thermostart switch/ radiator fan switch
i had faced this problem in my zen and juss got the switch changed
and my problem was solved... try it out sometimes the fam use to work some time was not functioning because of which all my coolant had leaked out...

Some amount of research has lead me to the conclusion that a drop in the fuel level in the tank leads to the rough idling and overheating. I drove the car in very 'decent' manner. So decent that it was returning an FE of more than 16 kmpl in city driving conditions. Later topped up the tank and found that niether does the vehicle overheat nor does it have rough idling. Tried this for the second time, and by the time the fuel gauge got below half, I started experiencing the same vibrations and slight overheating.

How does the amount of fuel in the tank affect refinement and cooling?

Check your fuel pump for blockages on the filter (this however would not be affected by the fuel level) else you might have a fuel pump that is leaking inside the tank and gets affected (loses fuel pressure) when you fuel level drops. We faced this recently with a Cielo here, had to replace the pump and the car came back to normal again.